Cotton bollworm (Helicoverpa armigera Hubner) and native bud worm (Helicoverpa punctigera Wallengren) are the major pests of cotton. Both insects are polyphagous and they feed preferentially on young growing tips or reproductive structures. The adults feed on nectar and the damage they cause is the result of the larvae feeding on leaves and buds or bolls. Infestations of these moths results in the loss of the terminal bud or fruiting structures either as floral buds (squares) or as fruit (bolls) causing considerable yield loss. Host plants other than cotton include maize, sorghum, wheat, sunflower, lucerne, various legumes especially soybean, pigeon pea and chickpea, tomatoes, okra, other vegetables, fruits, top fruits and citrus.
H. armigera is cosmopolitan and is the principal species in the Old World from Africa to the Pacific Islands but H. punctigera is an endemic species. Infestation of cotton by Helicoverpa spp. may occur at anytime after seedling emergence, but their abundance is highly variable being influenced by environmental factors, natural enemy abundance, quality and quantity of host plants and also their migratory movements. The two species usually follow a regular pattern of abundance in all areas they attack with H. punctigera the dominant species prior to flowering and well into summer (January). H. armigera becomes dominant from January onwards in most areas and is rarely seen in early season cotton.
The current control programme for cotton bollworm and native budworm in cotton relies heavily on synthetic insecticides. Cotton crops receive on average 12 insecticide and insecticide mixture sprays each season, although extremes of 18-20 sprays still occur. In 1991 Australian cotton growers spent approximately A$74 million on insecticides, A$15 million on application costs and A$9 million for professional consultants giving total insect control costs approaching A$100 million per year. The over-reliance on insecticides and its associated problems of insecticide resistance especially in H. armigera, disruption of natural enemies of the pests and environmental consequences due to residues in soil and water, off-target drift near human habitation have cast doubt on the long term viability of the cotton industry and the classical insecticide approach. It is therefore essential that an alternative non-chemical control measure be developed against the pest to achieve sustainability of cotton production.
Presently with our monoculture practices in agriculture and the use of pesticides we are inadvertently discriminating against beneficial insects. Many areas where crops are grown especially cotton growing areas are remote from wild vegetation. They are often treeless, bushless, rockless and often lay fallow most part of the year. With no natural refuges, no food sources for adult natural enemies of phytophagous insects, beneficial insects are made ineffective. There is therefore lack of diversity and instability in the agroecosystem.